1. Field of the Invention
The present invention is directed to methods for modelling tertiary (three-dimensional) structures of biologically active ligands, to methods for designing and synthesizing agonists and antagonists to the ligands based on the three-dimensional models generated for such ligands, and to the model itself generated for Angiotensin II from the methods of this invention.
2. State of the Art
In the field of chemistry, compounds can be defined in several ways. For example, a compound can be defined by its empirical formula, e.g., in the case of n-hexane the empirical formula would simply be C.sub.6 H.sub.14. For simple molecules such as water, methane, carbon dioxide, etc., the empirical formula can provide useful information.
However, as the complexity of the molecule increases, the empirical formula must be complemented by structural information concerning the covalent bonding of the individual atoms vis-a-vis each other in order to derive meaningful information concerning the molecule. Such information is generally depicted as a two-dimensional representation (primary structure) of the covalent bonds between the respective atoms. Such primary structures are well known pictorial representations of the compound of interest. These representations are usually defined as the structural formula of the compound which, for example, in the case of say n-hexane would be represented as: ##STR1## However, even with the molecule's structural formula, valuable information is still missing regarding the position in three-dimensional space of the individual atoms relative to each other. Such three-dimensional structures or conformations for a molecule are determined in part by non-covalent interactions, e.g., electrostatic and non-electrostatic interactions such as ionic interactions, hydrogen bonding, Van der Waal forces, etc., between different atoms of the molecule.
Three-dimensional information, i.e. , the ligand's conformation, is extremely valuable for naturally occurring biologically active ligands. In particular, such biologically active ligands generally have one or more active sites on or within the molecular structure of the ligand. Such active sites can involve a charge-transfer interaction (as later defined). When such a ligand is bound to its complementary receptor molecule, the active site activates the receptor molecule thereby affecting the biological activity of the receptor molecule. Thus, activation of the active site, whether by a charge-transfer interaction mechanism or by some other mechanism, is generally a necessary step in affecting the biological activity of the receptor. Further in this regard, if it were possible to create an accurate three-dimensional model of the naturally occurring biologically active ligand [including its active site(s)] as found in vivo, then such models could be used to create mimetics, e.g., agonists and antagonists, of such ligands. For example, if it is desirable to suppress the biological activity of the receptor in vivo, then an accurate three-dimensional model of the receptor's naturally occurring complementary ligand including its active site(s), would greatly facilitate the preparation of antagonists to this receptor. Likewise, an accurate three-dimensional model of the ligand of interest would also facilitate the design and synthesis of agonists when it is desirable to increase or to stimulate the biological activity of the receptor in vivo.
While three-dimensional models have heretofore been proposed for molecules including ligands, such three-dimensional representations have suffered from one or more serious drawbacks, particularly as they relate to biologically active ligands having active site(s) which employ a charge-transfer interaction. In particular, such prior art methods have failed to provide a simple means to identify the active site(s) of such ligands. Accordingly, in such cases, the creation of a three-dimensional model of such a ligand including its active site was generally conducted by extremely laborious procedures such as structure-activity relationships, theoretical considerations, etc. However, because such procedures are unable to identify a charge-transfer interaction at the active site of these ligands, it has not been possible to model mimetics of such ligands to a meaningful conformation.
Additionally, other art recognized methods of modelling the tertiary structure of a compound in three-dimensional space, such as x-ray crystallography, have the drawback that with biologically active ligands, the steps required to prepare the ligand for analysis can change the ligand's tertiary structure and accordingly, the structure as determined by this analysis may not conform to the structure found in vivo. Moreover, not all biologically active ligands are amenable to such analysis.
In view of the above, it is an object of this invention to develop a process which would model the three-dimensional spatial (tertiary) structure of a biologically active ligand having one or more active sites employing a charge-transfer interaction. It is a further object of this invention that this modelling identify the chemical groups at the site(s) of charge-transfer interactions. It is still a further object of this invention to create models of such ligands closely resembling the structure of the ligand found in vivo. It is still another object of this invention to design mimetics to such ligands by reference to the model generated for the ligand. These and other objects are achieved by the present invention as evidenced by the attached summary of the invention, detailed description of the invention, examples and claims.